aaron.ballman added inline comments.
================
Comment at: clang/include/clang/Basic/Attr.td:4133
+def NoUnwind : DeclOrStmtAttr {
+ let Spellings = [Clang<"nounwind", /*allowInC =*/0>];
+ let Accessors = [Accessor<"isClangNoUnwind", [CXX11<"clang", "nounwind">]>];
----------------
lebedev.ri wrote:
> aaron.ballman wrote:
> > Should this be allowed in C (where structured exception handling is still a
> > thing)?
> The only two thing about structured exceptions i know
> is that it's abbreviation and that it's a MSVC thing.
> I don't know anything about how "exceptions" work there,
> and therefore i do not want to touch it.
>
> https://llvm.org/docs/LangRef.html notes:
> ```
> nounwind
> This function attribute indicates that the function never raises an
> exception. <...>.
> However, functions marked nounwind may still trap or generate asynchronous
> exceptions.
> Exception handling schemes that are recognized by LLVM to handle asynchronous
> exceptions,
> such as SEH, will still provide their implementation defined semantics.
> ```
Okay, let's leave it as-is for now and we can relax the restriction later if we
find a need.
================
Comment at: clang/include/clang/Basic/Attr.td:4138
+ "functions and statements">;
+ let SimpleHandler = 1;
+}
----------------
lebedev.ri wrote:
> aaron.ballman wrote:
> > I would have guessed we'd want to help the user out in a case like:
> > `[[clang::nounwind]] void func() noexcept(false);`, given that this stuff
> > can creep in via macros?
> Could you please clarify, what do you mean by "help the user" in this case?
> Given
> ```
> [[clang::nounwind]] void func() noexcept(false);
>
> void qqq();
>
> void foo() {
> try {
> func();
> } catch (...) {
> qqq();
> }
> }
> ```
> we already end up with
> ```
> ; Function Attrs: mustprogress noinline nounwind optnone uwtable
> define dso_local void @_Z3foov() #0 {
> entry:
> call void @_Z4funcv() #2
> ret void
> }
>
> ; Function Attrs: nounwind
> declare void @_Z4funcv() #1
>
> attributes #0 = { mustprogress noinline nounwind optnone uwtable
> "frame-pointer"="all" "min-legal-vector-width"="0" "no-trapping-math"="true"
> "stack-protector-buffer-size"="8" "target-cpu"="x86-64"
> "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
> attributes #1 = { nounwind "frame-pointer"="all" "no-trapping-math"="true"
> "stack-protector-buffer-size"="8" "target-cpu"="x86-64"
> "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
> attributes #2 = { nounwind }
> ```
> and if i drop `[[clang::nounwind]]`, `landingpad` is back.
> Could you please clarify, what do you mean by "help the user" in this case?
The user has said "this function throws exceptions" (`noexcept(false)`) and
it's also said "this function never unwinds to its caller" (the attribute) and
these statements are in conflict with one another and likely signify user
confusion. I would have expected a warning diagnostic here.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D138958/new/
https://reviews.llvm.org/D138958
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